Full flow mechanical failsafe

ABSTRACT

A full-flow mechanical failsafe ( 100 ) is composed of a cylindrical shell ( 101 ) having a movable sealing plug ( 105 ) therein, for attachment to a filter element ( 110 ) of a fluid filtering system, such as a gas clean up system in a power plant. The sealing plug ( 105 ) rests on locking spheres ( 107 ) within the shell ( 101 ) during normal operation. Upon filter failure or breakage, the flow fluid will be substantially increased, causing an increase in upward pressure against the sealing plug ( 105 ), forcing it upward off the spheres ( 107 ) and into sealing contact with a flow aperture ( 102, 103 ), shutting off fluid flow. The spheres ( 107 ) move downward into a locking position upon movement of the sealing plug ( 105 ), to secure the sealing plug ( 105 ) in its upward sealing position. The failsafe ( 100 ) can be used in fluid flow control systems other than fluid filtering systems, such as oil or gas pipelines, and can be used to prevent improper reverse fluid flow.

This application claims the benefit of provisional application Ser. No.60/153,223 filed Sep. 13, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to fluid flow control systems, and tomechanical failsafes or shut-off devices for preventing the flow offluids (e.g., gas or liquid streams) upon breakage or failure ofcomponents in the system, such as filters or other components. Moreparticularly, the invention relates to devices for preventing the flowof high-temperature (e.g., up to 1800° F.) gas streams upon filterdamage.

2. Description of Background Art

Industrial systems in which fluids flow (such as gas turbine powerplants, liquid fuel processing plants, hydraulic systems, pneumaticsystems and the like), and in which gases are usually cleansed ofentrained particulate matter or treated prior to coming into contactwith system components that are susceptible to such particulate matter,usually provide filtration for removing impurities and/or restrictingflow to system design levels. To prevent damage to system componentsand/or the environment, such systems often are provided with flowlimiting or shut-off valve mechanisms. Upon the occurrence of damage,breakage or removal of filter components, these shut-off mechanisms stopthe flow of fluid through the system.

In particular, high temperature and high pressure barrier filter systemsare critical to the successful commercialization of PFBC and IGCCcoal-based power plant systems. Presently the most commercially readybarrier filter systems are based on candle filter technology. Thesebarrier filter systems generally employ a large number of individual,porous candle filter elements in parallel.

Pilot-scale candle filter-based systems have been shown to removeparticulate matter down to a concentration of less than 1 ppm (part permillion) when in good operating condition. However, in the event of thefailure of even a single filter element, the filter system outlet dustloading will increase and thereby potentially damage gas turbine blades,contaminate other downstream processes, and limit the availability ofthe power system. A filter failure safeguard device which would preventthe flow of particle-laden gas through the failed filter elementlocation would serve to minimize the potential damage to downstreamequipment, minimize dust emissions, and allow the power plant tocontinue operation until a convenient or scheduled outage can beimplemented.

Various types of flow limiting/shut-off mechanisms are known in theprior art, see e.g., U.S. Pat. Nos. 5,242,581; 3,261,146; 2,892,512;2,833,117; 2,687,745; 2,680,451; 2,635,629; 1,983,791. Such mechanismsare characterized by their complicated structure, large number of movingparts, difficulty in installation, limited operational temperatureranges, and/or dependence on entrained particle concentration foractivation of the shut-off feature.

There remains a need in the art for improvement to the structure ofmechanical fluid flow shut-off devices.

SUMMARY OF THE INVENTION

The present invention provides an improvement to the prior art, byproviding according to one embodiment a full-flow failsafe, including afilter element for filtering entrained particles from a flowing fluidstream, a shell having apertures at each end thereof for enabling thefluid stream to flow therethrough, a first one of the apertures beingcoupled to the filter element, a sealing plug movably positioned withinthe shell, the sealing plug being oriented in a first position duringnormal operation of the filter element to permit fluid flow through theshell, and, upon failure or breakage of the filter element, being movedby increased fluid velocity to a second position wherein the sealingplug forms a sealing contact with a second one of the apertures, and alocking mechanism supporting the sealing plug in the first position, andbeing moved to a locking position for securing the sealing plug in thesecond position in response to the movement of the sealing plug.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood from the detaileddescription given below in conjunction with the accompanying drawings.These are provided by way of illustration only and are not intended aslimiting the present invention, and wherein:

FIG. 1 is a cross-sectional diagram of a full-flow mechanical failsafe100 according to a preferred embodiment of the invention, in an inactivemode of operation (allowing normal fluid flow);

FIG. 2 is a cross-sectional diagram of full-flow mechanical failsafeaccording to the invention in an active mode of operation, whichprevents the flow of fluid through a damaged filter element 301;

FIG. 3 is a top view of the sloped bottom surface of the failsafe shell,showing the presence of grooves 109 for locking spheres 107 (only one ofwhich is shown);

FIG. 4 is a side view of sealing plug 105 with a hemispherical sealingsurface 310, with an enlarged sectional view of conical surface 201showing the presence of a concave indentation 202 for maintaininglocking spheres 107 in place in the inactive mode; and

FIG. 5 is a top view of frame 316 which secures alignment pin 205 to theshell 101 and establishes proper positioning of the alignment pin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the full-flow mechanical failsafe according to oneembodiment of the present invention is particularly adapted for candlefilter systems including candle filters 110. Such candle filter systemswould be used, for example, in power plants for removing dust and othersolid particle pollutants or contaminants from gases at temperatures upto approximately 1650° F. flowing through various stages of the powerplant equipment.

There are two primary causes for dust to reach the clean side ofcandle-based filter systems. The first is the existence of small leaksaround filter element gaskets or seals resulting from faulty gasketcomponents or improper installation. In such an instance the flow pathof dust-laden gas leaking across the tubesheet 302 would bypass thecandle filter element 110 and its safeguard device. The only remedy fora failure of this type is prevention through quality control of gasketmaterials and installation procedures.

The second cause is the case wherein solid particles breach thetubesheet 302 as a result of catastrophic failure or breakage of one ormore candle filter elements 110. Failures of this type have beenexperienced at many pilot- and demonstration-scale Hot Gas Cleanup(HGCU) filter systems, and present the primary challenge for systemreliability that is addressed by the present invention.

The mechanical failsafe device 100 according to one preferred embodimentof the present invention includes a cylindrical shell 101, about 3inches in diameter and about 4 to 5 inches in height. Apertures 102 and103 are centered at the top and bottom of the shell 101, and allowfiltered flue gas to flow upward through the device in a flow directionindicated by arrows 104 during normal operation, and pulse cleaning gasto flow downward through the device in an opposite direction, when anintact and operational filter element 110 is connected to the failsafe.

A sealing plug 105 is provided in the interior of the cylindrical shell101. Sealing plug 105 is essentially in the shape of a hemisphere joinedon its lower flat surface to the flat surface of a cone of equaldiameter to the hemisphere. The sealing plug 105 is supported in theshell by three locking spheres 107, (only one of which is shown forsimplicity) preferably positioned 120° from each other around theconical portion of the sealing plug. The spheres rest in grooves orchannels 109 in a conical surface 108 in the shell interior, and alsocontact inner angled surface 311 of the shell 101. As shown in FIG. 3,the grooves 109 are cut into the surfaces 108 under the spheres 107 toguide their movement when the mechanical failsafe is activated, asexplained further below. Additionally, as shown in FIG. 4, a continuousindentation 202 is formed around the circumference of the lower surface201 of the sealing plug, at a position where the indentation 202contacts the spheres as shown in FIG. 1, to assist in holding thesealing plug in the inactive position during the occurrence ofvibrations that may be experienced in the filter vessel duringinstallation and normal operation.

The diameter of the spheres 107, the dimensions of the shell 101, thesealing plug 105, the conical surfaces 108 and 201, the apertures 102,103 and the annular gap 304 between the inner surface of the shell 101and the sealing plug 105 at its widest dimension are designed such that,with the normal flowrate of filtered gas upward through the failsafe,the upward pressure on the sealing plug 105 will not be sufficient tocause the sealing plug 105 to be lifted from its resting position on thespheres 107 when the filter element 110 is intact. The weight of thesealing plug 105 can be selected during design by adjusting the size ofthe internal volume 303, or in other words a portion of the interior ofthe sealing plug may be solid to establish the optimum weight to ensurethe proper stability of the plug on the spheres during normal operationfor the particular flow parameters of the system on which it isinstalled.

In the preferred embodiment as shown in FIGS. 1, 2 and 4, thehemispherical portion 312 of the plug is provided as a piece separatefrom the conical portion 313. This allows the amount of internal volume303 to be selected at the manufacturing stage, either by manufacturingconical portions 313 of varying internal volume, or by filling theinternal volume 303 with an appropriate amount of a suitable materialfor adjusting the weight of the sealing plug 105. The two pieces 310 and313 are then joined together. As shown in FIG. 1, a threaded connection314 may be provided for this purpose; other joining methods may be usedequivalently. The weight of the sealing plug also is determined by thedegree that the upward flow must increase (as would occur in a failure)in order to lift the sealing plug and activate the failsafe (as shown inFIG. 2). For a specific barrier filter installation application as shownin FIG. 1, the weight of the sealing plug and the dimension of the gap304 are set so that only the flowrate encountered in a failure of thefilter element will be sufficient to lift the sealing plug enough toactivate the failsafe device.

As shown in FIG. 1 the failsafe 100 is attached to the tubesheet 302with the aid of a mounting bracket or flange 114. Other attachmentmechanisms may be used, depending on the tubesheet design. A gasket 106a is provided between the failsafe and the filter, and an additionalgasket 106 b may be provided between the filter element 110 and thetubesheet 302. Gaskets 106 a and 106 b may be made of Nextel® or similarmaterial.

The shell 101 may be constructed from two separate pieces, joinedtogether at flange 307 or by other equivalent joining means, to enableinstallation and removal of the sealing plug and locking spheres.

The apertures 102, 103 and the annular gap 304 should be sized such thatsufficient flow paths are maintained within the failsafe for the passageof filtered flue gas and pulse cleaning gas to minimize the addition offlow resistance to the system by the failsafe during either filtering orpulse cleaning operations.

In the inactive (e.g., normal) mode of operation, the upward flow 104 offiltered flue gas provides an increased pressure in the lower portion ofthe failsafe 100, having a magnitude determined by the velocity v andthe density μ of the gas according to Bernoulli's term ½ ρ². A largeproportion of this pressure will be dissipated across the annular gap304. Constrictions in the annular gap act as an annular orifice for gasflow; the smaller this annular orifice, the more pressure is dissipatedas the gas passes through it.

During application of reverse gas pulses used to clean the filterelements, or in other cases where download flow is the normal flowdirection, the downward pressure exerted on the plug by the flow 305from such pulses, or flow, is transferred through the spheres 107 to theinner wall 311 and the sloped inner surface 108 of the shell.

When the filter element 301 breaks, as shown in FIG. 2, two conditionschange in the vicinity of the mechanical failsafe 100. The first is thatthe upward velocity of the gas through the remaining part of the brokenfilter element and the mechanical failsafe increases very rapidly,driven by the tubesheet pressure drop (not shown) at the time ofbreakage. The second is that particle-laden or unfiltered or untreatedgas advances from the point of breakage of the filter element 301towards the top of the candle filter element and the mechanical failsafe100. Because the failsafe desirably is activated almost instantaneouslyin response to the rapid increase of upward gas velocity experienced ina filter element failure, little or no particle-laden gas or untreatedgas is expected to exit the top of the failsafe before the failsafe isfully activated and the flow of gas is shut off.

In the event of filter element breakage, the increased gas velocitythrough the mechanical failsafe 100 creates a significantly higherpressure drop across the annular orifices around the sealing plug,thereby significantly increasing the upward pressure on the sealing plugitself. The degree to which the velocity of the gas entering themechanical failsafe will be increased upon the breakage of a filterelement is primarily dependent upon the tubesheet pressure drop and thedimensions of the portion of the broken filter element that remainsattached to the tubesheet. Calculations have indicated that, followingthe breakage of a filter element, the velocity of gas through themechanical failsafe could be increased by a factor of 10 or more (withthe concomitant increase of upward pressure on the sealing plugincreasing by a factor of 100 or more).

Upon the occurrence of a sufficiently higher pressure drop across theannular orifice around the sealing plug, as would happen upon thebreakage of a filter element 301, the increased upward gas pressure onthe sealing plug will lift the sealing plug up from its resting positionon the spheres. The plug will continue to move upward until it contactsthe upper sealing surface 306 around the upper aperture 102, as shown inFIG. 2. The diameter of this upper sealing surface is made equal to thediameter of the hemispherical surface of the sealing plug, so that ahigh-quality seal will be formed when these two surfaces contact eachother in the activated mode as shown in FIG. 2.

As shown in FIG. 1, the interior of the shell 101 can be shaped suchthat the pressure across the annular orifice adjacent to the widestportion of the sealing plug would increase as the plug travels upward bymaking the annular gap smaller as the plug nears the sealing surface 306at the top of the shell 101.

Once the sealing plug reaches the top of the shell and fully contactsthe sealing surface 306, the gas flow is completely blocked and theupward force is reduced to zero. Just before this time, the spheres 107begin to roll down the inclined surface 108 in a straight directionaided by the grooves 109, as shown in FIG. 2, until the spheres becomepinched in position at the bottom of the sealing plug 105 at location319, between the plug and the grooves 109 in the inclined surface of theshell. In this regard the dimensions of the spheres, shell and sealingplug are designed to prevent the spheres from falling down through theaperture 103 at the bottom of the shell (see FIG. 1). When the spheresreach their final position as shown in FIG. 2, they serve as lockssecuring the sealing plug against the sealing surface 306 of the upperaperture 102 of the shell, to thereby prevent the flow of dust and/oruntreated gas past the failsafe, and also to prevent the sealing plugfrom being forced back down into the shell by the pressure from reverseflow gas cleaning pulses.

As shown in FIG. 2, an optional axial alignment pin 205 may be attachedto the top of the shell and extends into the body of the sealing plugthrough a close tolerance guide hole 308 and through the body into asecond guide hole 309. As shown in FIG. 5, the alignment pin may beattached to the top of the shell with a frame 316 through a threadedconnection 318. The frame 316 may be attached to the shell with screws317. The alignment pin alternatively may be attached to the sealing plugand extend through guide holes in the shell. The alignment pin 205assists in the proper seating of the sealing plug against the sealingsurface 306 of the shell.

Further, during installation in the filter vessel, a small amount ofparaffin may be used to hold the sealing plug and spheres in theirproper positions within the shell by application to the contactingsurfaces of the spheres. The paraffin would melt and burn off as thefilter system is preheated during a system startup process.Reapplication of paraffin would be unnecessary except where a failsafehad to be removed, reconditioned and reinstalled after activation by thefailure of its filter element.

The full-flow mechanical failsafe of the present invention providesseveral advantages over failsafe devices that make use of entrainedparticles in the flowing gas to form a seal. The formation of a seal byusing such entrained particles takes place gradually, whereas themechanical failsafe of the invention shuts off the flow ofparticle-laden gas almost immediately upon filter breakage. Theeffectiveness of the mechanical failsafe is thus independent of particleconcentration. Further, seals that depend on plugging of flow paths byentrained particles can be compromised by the application of periodicreverse flow cleaning gas pulses. In contrast, the failsafe of thepresent invention provides a positive seal against the force exerted bysuch cleaning pulses. In the event a failure occurs during applicationof a cleaning pulse, the failsafe will be activated as soon as thenormal fluid flow direction is reestablished.

Reconditioning of activated failsafes is fairly simple. All componentsare preferably made of suitable material (such as 310 SS steel, which iswell suited to HGCU filter applications) which can be washed, dried,reconfigured in an inactive mode, and reinstalled.

The basic principles of the full-flow mechanical failsafe may be adaptedin alternate embodiments for applications other than HGCU particlefiltration. For example, similar devices of much larger scale may beused in an oil or gas pipeline. The failsafe devices would be positionedat periodic intervals along such pipelines, in short vertical runs wherethe flow direction is upward. In the event of pipeline failure, thefluid flow would increase most immediately upstream from the failsafedevice, activating it and shutting off the flow, thus mininizing fluidloss as well as potential safety and environmental hazards.

Another alternate embodiment of the invention could be configured suchthat even a small upward flow of fluid would activate the device. Thisembodiment would be useful to prevent backward flow in a system wherethe normal fluid flow direction was downward.

The invention having been thus described, it be apparent to thoseskilled in the art that the same may be varied in many ways withoutdeparting from the spirit and scope of the invention. Accordingly, anyand all such modifications are intended to be covered by the followingclaims.

What is claimed is:
 1. A full-flow failsafe, comprising: a filterelement for filtering entrained particles from a flowing fluid stream; ashell having apertures at each end thereof for enabling said fluidstream to flow therethrough, a first one of said apertures being coupledto said filter element; a sealing plug movably positioned within saidshell, said sealing plug being oriented in a first position duringnormal operation of said filter element to permit fluid flow throughsaid shell, and being moved by increased fluid velocity to a secondposition wherein said sealing plug forms a sealing contact with a secondone of said apertures, upon failure or breakage of said filter element;and at least one locking mechanism supporting said sealing plug in saidfirst position, and being moved to a locking position for securing saidsealing plug in said second position in response to said movement ofsaid sealing plug.
 2. A full-flow failsafe as set forth in claim 1,wherein said locking mechanism comprises a sphere.
 3. A full-flowfailsafe as set forth in claim 2, wherein a bottom interior surface ofsaid shell is sloped, and said sphere rolls downward between saidsealing plug and said sloped surface to a locking position locking saidsealing plug in sealing contact with said second aperture upon saidmovement of said sealing plug.
 4. A full-flow failsafe as set forth inclaim 3, further comprising two additional spheres located around abottom surface of said sealing plug.
 5. A full-flow failsafe as setforth in claim 3, further comprising a groove cut into said slopingsurface to guide movement of said sphere.
 6. A full-flow failsafe as setforth in claim 3, further comprising an indentation in a surface of saidsealing plug contacting said sphere, to hold said sphere in place duringnormal operating conditions of said filter element.
 7. A full-flowfailsafe as set forth in claim 1, further comprising an alignment pinmounted on said shell to maintain alignment of sealing plug with respectto said second aperture upon movement of said plug into contact withsaid second aperture.
 8. A full-flow failsafe as set forth in claim 1,wherein the interior of said shell is dimensioned to cause upwardpressure against said sealing plug to increase as said sealing plugadvances toward said second aperture upon filter failure or breakage. 9.A full-flow failsafe as set forth in claim 1, further comprising asealing gasket mounted within said second aperture.
 10. A full-flowfailsafe as set forth in claim 1, wherein said fluid is a gas.
 11. Afull-flow failsafe as set forth in claim 1, wherein said filter elementis a candle filter.
 12. A full-flow failsafe for a fluid flow system,comprising: a shell having apertures at each end thereof for enabling afluid stream to flow therethrough, a first one of said aperturesadmitting a fluid stream into the failsafe, and a second one of saidapertures allowing said fluid stream to exit said failsafe; a sealingplug movably positioned within said shell, said sealing plug beingoriented in a first position during normal fluid flow of said system topermit fluid flow through said shell, and being moved by increased fluidvelocity to a second position wherein said sealing plug forms a sealingcontact with said second one of said apertures, said increased fluidvelocity being of a magnitude indicative of improper operation of saidsystem; and at least one locking mechanism supporting said sealing plugin said first position, and being moved to a locking position forsecuring said sealing plug in said second position in response to saidmovement of said sealing plug.
 13. A full-flow failsafe as set forth inclaim 12, wherein said locking mechanism comprises a sphere.
 14. Afull-flow failsafe as set forth in claim 13, wherein a bottom interiorsurface of said shell is sloped, and said sphere rolls downward betweensaid sealing plug and said sloped surface to a locking position lockingsaid sealing plug in sealing contact with said second aperture upon saidmovement of said sealing plug.
 15. A full-flow failsafe as set forth inclaim 14, further comprising two additional spheres located around abottom surface of said sealing plug.
 16. A full-flow failsafe as setforth in claim 14, further comprising a groove cut into said slopingsurface to guide movement of said sphere.
 17. A full-flow failsafe asset forth in claim 14, further comprising an indentation in a surface ofsaid sealing plug contacting said sphere, to hold said sphere in placeduring normal operating conditions of said fluid flow system.
 18. Afull-flow failsafe as set forth in claim 12, further comprising analignment pin mounted on said shell to maintain alignment of sealingplug with respect to said second aperture upon movement of said pluginto contact with said second aperture.
 19. A full-flow failsafe as setforth in claim 12, wherein the interior of said shell is dimensioned tocause upward pressure against said sealing plug to increase as saidsealing plug advances toward said second aperture upon abnormalincreased fluid flow.
 20. A full-flow failsafe as set forth in claim 12,wherein said fluid is a gas.
 21. A full-flow failsafe as set forth inclaim 12, wherein said fluid is a liquid.
 22. A full-flow failsafe asset forth in claim 1, wherein said sealing plug includes a slopedsurface on a lower portion thereof.
 23. A full-flow failsafe as setforth in claim 12, wherein said sealing plug includes a sloped surfaceon a lower portion thereof.